To realize microscopic miniaturization of electronic devices, improvement in accuracy and quality of the techniques used for the measurement and fabrication of extremely fine regions of semiconductor elements is an indispensable requirement. With a view to improving the productivity of electronic devices and the freedom of design thereof, the formation of a required pattern on a semiconductor material has been effected by a method which involves application of a photo-mask to the surface of the material or a method which involves direct irradiation of the surface of the material with electron beams. The optical lithographic method, which is simpler in both mechanical construction and operational procedure than the aforementioned method using photo mask or electron beams, should find acceptance.
Generally, as means for reading optical information from extremely minute regions of a given object by scanning, there have been developed a flying-spot scanner which utilizes the light-emitting surface of a CRT, a drum scanner which uses a rotary drum, and a laser microscope. As devices for forming a given image of extremely fine details on the surface of a minute substrate, there have been developed and accepted for actual use a laser trimming device and a laser-processing device, for example.
The methods of scanning adopted in these devices may be broadly classified into a type resorting to mechanical driving of stages on which objects being scanned are mounted, a type wherein the position of light sources are changed with the aid of movable mirrors, and a type utilizing the light-emitting surface of a CRT.
The method which mechanically scans the object has the disadvantage that the inertia, vibration and other similar impacts produced while the object being scanned and the device serving to retain intact the environment of the object are in motion during the mechanical scanning can directly result in the degradation of the resolution and the reproducibility of measurement. With this method, therefore, it has been difficult to obtain desired measurement and fabrication at extremely low temperatures and high vacuum which necessitate adoption of particularly complicated devices for the maintenance of environment.
To preclude the disadvantage due to the inertia, vibration, and other impacts produced in the mechanical elements, there has been proposed a technique which makes use of optical fibers of small inertial mass (British Pat. No. 1,124,805). In the conventional scanning mechanism which utilizes optical fibers, however, the loci of the movement of the fiber tips fall in a spherical surface, the relative position of fibers to the object lens varies, and the fibers produce a nonlinear movement involving different rates of speed in the central portion and in the peripheral portion. By this reason, such optical fibers are not well suited for use in devices used for the measurement and fabrication of semiconductor element materials which call for accuracy of much higher level. They are totally unsuitable for spectromicroscopes, exposure devices, and other similar devices which require high resolution and high quantitative accuracy.
In the method which effects the scanning with laser beams by means of movable mirrors, perfect alignment of one optical system for projection with one for image-pickup calls for use of half mirrors. Thus, the efficiency of image-pickup is inevitably lowered. Moreover, the complicated optical configuration consisting of a laser unit, half mirrors, movable mirrors, mirrors for the guidance of laser beams, and the like, requires additional adjustment. This method has proved disadvantageous in terms of maintenance and operation.
The method which utilizes the light-emitting surface of a CRT has the disadvantage that the light source has a lower intensity than the laser unit and the light emitted is not easily focused. This method, therefore, has found limited applications.